/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package nlp;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

//import org.apache.hadoop.classification.InterfaceAudience;
//import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FSDataInputStream;
import org.apache.hadoop.fs.FileStatus;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.InputSplit;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.JobContext;
import org.apache.hadoop.mapreduce.RecordReader;
import org.apache.hadoop.mapreduce.TaskAttemptContext;
import org.apache.hadoop.util.LineReader;
import org.apache.hadoop.mapreduce.lib.input.FileSplit;
import org.apache.hadoop.mapreduce.lib.input.LineRecordReader;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;

/**
 * NLineInputFormat which splits N lines of input as one split.
 * 
 * In many "pleasantly" parallel applications, each process/mapper processes the
 * same input file (s), but with computations are controlled by different
 * parameters.(Referred to as "parameter sweeps"). One way to achieve this, is
 * to specify a set of parameters (one set per line) as input in a control file
 * (which is the input path to the map-reduce application, where as the input
 * dataset is specified via a config variable in JobConf.).
 * 
 * The NLineInputFormat can be used in such applications, that splits the input
 * file such that by default, one line is fed as a value to one map task, and
 * key is the offset. i.e. (k,v) is (LongWritable, Text). The location hints
 * will span the whole mapred cluster.
 */
// @InterfaceAudience.Public
// @InterfaceStability.Stable
public class NLineInputFormat extends FileInputFormat<LongWritable, Text> {
	public static final String LINES_PER_MAP = "mapreduce.input.lineinputformat.linespermap";

	public RecordReader<LongWritable, Text> createRecordReader(
			InputSplit genericSplit, TaskAttemptContext context)
			throws IOException {
		context.setStatus(genericSplit.toString());
		return new LineRecordReader();
	}

	/**
	 * Logically splits the set of input files for the job, splits N lines of
	 * the input as one split.
	 * 
	 * @see FileInputFormat#getSplits(JobContext)
	 */
	public List<InputSplit> getSplits(JobContext job) throws IOException {
		List<InputSplit> splits = new ArrayList<InputSplit>();
		int numLinesPerSplit = getNumLinesPerSplit(job);
		for (FileStatus status : listStatus(job)) {
			splits.addAll(getSplitsForFile(status, job.getConfiguration(),
					numLinesPerSplit));
		}
		return splits;
	}

	public static List<FileSplit> getSplitsForFile(FileStatus status,
			Configuration conf, int numLinesPerSplit) throws IOException {
		List<FileSplit> splits = new ArrayList<FileSplit>();
		Path fileName = status.getPath();
		if (status.isDir()) {
			throw new IOException("Not a file: " + fileName);
		}
		FileSystem fs = fileName.getFileSystem(conf);
		LineReader lr = null;
		try {
			FSDataInputStream in = fs.open(fileName);
			lr = new LineReader(in, conf);
			Text line = new Text();
			int numLines = 0;
			long begin = 0;
			long length = 0;
			int num = -1;
			while ((num = lr.readLine(line)) > 0) {
				numLines++;
				length += num;
				if (numLines == numLinesPerSplit) {
					// NLineInputFormat uses LineRecordReader, which always
					// reads
					// (and consumes) at least one character out of its upper
					// split
					// boundary. So to make sure that each mapper gets N lines,
					// we
					// move back the upper split limits of each split
					// by one character here.
					if (begin == 0) {
						splits.add(new FileSplit(fileName, begin, length - 1,
								new String[] {}));
					} else {
						splits.add(new FileSplit(fileName, begin - 1, length,
								new String[] {}));
					}
					begin += length;
					length = 0;
					numLines = 0;
				}
			}
			if (numLines != 0) {
				splits.add(new FileSplit(fileName, begin, length,
						new String[] {}));
			}
		} finally {
			if (lr != null) {
				lr.close();
			}
		}
		return splits;
	}

	/**
	 * Set the number of lines per split
	 * 
	 * @param job
	 *            the job to modify
	 * @param numLines
	 *            the number of lines per split
	 */
	public static void setNumLinesPerSplit(Job job, int numLines) {
		job.getConfiguration().setInt(LINES_PER_MAP, numLines);
	}

	/**
	 * Get the number of lines per split
	 * 
	 * @param job
	 *            the job
	 * @return the number of lines per split
	 */
	public static int getNumLinesPerSplit(JobContext job) {
		return job.getConfiguration().getInt(LINES_PER_MAP, 1);
	}
}
